Composite cryptomatte video
Png does not work with cryptomatte, as it requires a 32bit float precision which PNG can not provide.
You must use EXR in float32bit !
Blender will save out either a OpenEXR or OpenEXR multilayer. If you want all layers in one EXR file per frame, choose the multipayer option.
If you wish to save out multiple EXR per pass (Diffuse, Specular, Crypto ..) you must do via the Compositor &quot;File Output&quot; Node.
Apparently Blender will not render out multiple passes as EXR unless from inside the compositor. See also this answer here:
Save all render passes to EXR image?